Secondary amenorrhea, the absence of menstrual periods after normal menarche has occurred is very common among female athletes.Amenorrhea is a major concern for the athlete, primarily because of the health problems associated with it. Osteoporosis is one of the main medical concerns for the amenorrheic athelete. Amenorrhea may also negatively affect female reproductive ability and place the individual at an increased risk for endometrial hyperplasia and adenocarcinoma. Due to these serious health problems, researchers have attempted to define possible risk factors which would increase a woman's chance of becoming amenorrhea. There is disagreement as to whether or not amenorrheic runners are physiologically able to become more metabollically efficient when compared to eumenorrheic runners. The purpose of this study is to assess the metabolic status of both amenorrheic runners and eumenorrheic runners and to compare the findings. Specifically the following will be tests. Total energy expenditure in the amenorrheic group will be lower than that of the eumenorrheic group. This value will be determined through calculations involving values obtained from the the thermal effect of a meal and energy expended during exercise. Activity diaries will also be examined and included in the calculation. Component of total energy expenditure will be lower in the amenorrheic group when compared with the eumenorrheic group. In order to determine this, we will measure the resting metabolic rate, the energy expended during exercise and data obtained from an activity diary. The amenorrheic group will exhibit hormone levels which differ from that of the eumenorrheic group. We will measure FSH, LH, prolactin, TSH free triiodothyronine and free thyroxine. Energy intake in the amenorrheuc group will be lower than that of the eumenorrheic group. Reports have shown that most amenorrheic atheletes tend to report less intake than eumenorrheic atheletes. However, many investigators are suspicious of underreporting. By obtaining a dietary history, a 24 hour recall andf a three day food record over different days of the week, we hope to improve the validity of the dietary intake data.